Where do you live and what is the temperature of the cold water coming in?

A tankless system can only raise the temperature a certain amount, and in the winter, the incoming water can get close to freezing. In the summer, it can be 40-50 degrees warmer, so it can produce quite hot water then.

The things get calcium deposits in them too, which restricts their ability to raise the temperature. It might just need a good cleaning. You'd have to refer to the manual on how to do that. It could be it is fine and doing the best it can.

Tankless systems aren't for everyone, everywhere. You may need to learn to live with their limitations. Some can support a second one in series to raise the temperature more, or yours could just be undersized.

Use the search function and you'll get lots of reading material as this has been discussed fairly frequently here.

Tankless systems aren't for everyone, everywhere. You may need to learn to live with their limitations. Some can support a second one in series to raise the temperature more, or yours could just be undersized.

Perhaps it simply needs service.....

it all depends on where you live in the USA that will determine how well you like it

Thankless water heater make it take longer for you to get your hot water, since they don't start heating the water until you turn on the faucet. This problem can be solved by using a specialized pump, which in combination with the tankless unit can get your hot water to you at less than half the time it would take running the faucet full blast.

Thankless water heater make it take longer for you to get your hot water, since they don't start heating the water until you turn on the faucet. This problem can be solved by using a specialized pump, which in combination with the tankless unit can get your hot water to you at less than half the time it would take running the faucet full blast.

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The pump won't do anything unless there is a source of hot water, which there won't be if the tankless has been unused for a while. The pump systems used to provide instant hot water require a small electric water heater to supply that hot water. Circulating water to keep the water in the pipe hot wastes energy and in the summer it adds to the A/C load.

Circulating the water will do nothing about the problem of running out of hot water after two minutes.

If I had a tankless with inadequate capacity I would look for a place to put an electric tank heater between the tankless and the high-demand bathroom(s). The tankless would supply all of the makeup as long as it could keep up so the electric would have nothing to do except maintain temperature, which they do quite efficiently. If the tankless couldn't keep up with the demand then the electric would make that up when required.

With 40 gallons of hot water in an electric tank unit to start with, and the tankless doing its best to keep up, you would have a very good supply of hot water to meet any reasonable residential need.